Amplified D-104?

Not quite sure what to make of this I put it in chat forum instead of the technical forum just to be safe. http://www.ebay.com/itm/291821863260? he states it's a rare design hmm...The crap one sees on ebay.

I think that VELVAC thing is an automotive alarm buzzer or siren that makes the noise when it goes off. Whether it will pick up audio (voice) vibrations is unknown. It might.

I was one of the first ones back in the 1970's to use telephone earpieces and mouthpieces as replacement D104 elements so who knows. Nothing would surprise me. I've always wondered if I was responsible for people doing that now like the ones you see for sale on eBay. When CB'ers would bring me a bad D104 for repair I would tell them to just take their phone to the AT&T place and exchange it for another color phone, but to remove the ear and mouth pieces first. AT&T would never check and to just tell them you painted your house and needed another color phone. It wouldn't sound like a D104 anymore, but it worked and sounded a bit more like an amplified dynamic mic after. The earpieces actually worked better than the mouthpieces. With the amplifier that VELVAC piece might work.

OMFG ! Can you say MIDRANGE ? That would prolly punch thru any QRM or pileup! Freq response about 1K - 2K with a peak at 1500KC... HI HI

The thing actually sold for 42 bucks. Probably just for the base. Seller says "VERY RARE DESIGN" & " no way to test". I call "shenanigans" on that dude I think I'll start making some outrageous shit and try to sell it on Ebay.

I remember the guys who had the D104's where I used the telephone elements would often tell me that when they told people what they were using nobody would believe them. With the big 10 and 11-meter skip cycle in the 70’s and then again in the 80’s word may have gotten around. I may have not been the only one who ever tried it, but I’ve always wondered if it’s my fault or at least partially my fault for the ones you see on ebay now with the telephone earpiece elements .

I could not resist posting this and it just goes to show how technically dumbed down many hams are today.

This is one of those situations where the guy thinks he knows more than he actually does. He even blows it in the very beginning saying the circuit coverts it to powered. Well, if he really knew how amplifiers work and are configured compared to a simple source follower buffer which provides '0' gain then he might not have made a complete fool out of himself by positing what he did on the Internet.

The below is what I'm referring to. There is a slight mistake in the circuit because the 220-ohm drain resistor should not be there so even the other ham he was referring to knowlage was not 100% unless he was trying to reduce battery power consumption a bit and the 4V battery is in fact too small, but still. I highlighted the parts that are the funniest. I especially like the part where he says "You can tell, person who wrote article does not know what he is talking about, since he calls tubes boat anchors

"WARNING we have seen the above design on internet to use for a un powered D104. This is a bad design to convert it over to powered, lowZ, Bass response. No one, who really knows amplifier design, uses FET transistors, since they like to oscillate not amplify. BiPolar transistors want to amplify not oscillate, hence much better choice and the reason Astatic "the manufacturer" above used regular transistors in all its powered microphones.

You would be much better off to copy the original amplifier design, at the top of this article, that is proven to work correctly. Also you end up with adjustable level plus do not need rf chokes in effort to keep stable (not oscillate all the time "squeal").

You can tell, person who wrote article does not know what he is talking about, since he calls tubes boat anchors and designs for the use of +4 volt supply (Battery??). He needs to learn that when it comes to power and linearity tubes kill transistors every time and still do today. Your microwave oven is tube and only 4 inches square but delivers over a thousand watts of power. The most any transistor can deliver is 120 watts hence it would take 10 transistors with complicated combiner,large heat sink, drivers,pre drivers,oscillator etc.,etc. to accomplish the same task. Several transmitters at radio and TV stations TODAY that are over 1,000 watts use TUBE's. The most valuable and lowest distortion audio amplifiers are tube design (ask any audiophile today). Transistors are of value in low power circuit applications only. I believe it is only a matter of time until broadcast engineers rediscover "Space Modulation" which has been used for aircraft transmitters since 1948. A VOR (Variable Omni Range) ground based transmitter, for example and the most common, has 5 antennas total, not just one. A low power DSB signal to 4 of them in a phased array along with center one getting main high power carrier, can be ran Class E Tube and even more efficient, than hundreds of combined transistor types. Transistors running Class D have a much higher level of distortion and less reliability. Most people have heard of AM, FM & PM but very few SM. These stand for Amplitude Modulation, Frequency Modulation, Phase Modulation, Space Modulation respectfully.

In case someone reads this topic I want to clarify what the actual truth really is.

The D104 was invented back in the 1930's and the output impedance of the crystal cartridges where around 20Meg and possibly even greater at the time. All tube-type microphone inputs back then had very high input impedances so the D104 worked great. Up until about the late 1950's most transmitter microphone inputs were at least 1Meg until manufacturers started coming out with transceiver units which had much lower impedances. Business band radios and CB's for example and many with squelch control circuits. Many of those new transceivers had common audio sections where the mic amplifiers, modulators and the received output audio stages were the same stage and used for both. As a result, and especially the ones with squelch circuits the inputs started dividing off through other circuitry which greatly lowered the impedance. And because of the additional circuitry they started requiring some drive due to the loss it created. Microphone inputs suddenly decreased down to only around 5K to 6K. This became a huge change for what the D104 was originally designed for.

Astatic’s solution to the sudden impedance decrease and new drive requirement was to create the 2-transistor amplifier board below. That took the 20Meg and 10Meg crystal elements output down to the 5K to 6K output and drove the inputs with some amplification. The amplifier was never the greatest and it did create some distortion, but it worked good enough for the tube-type transceivers being made at the time along with many of the new SSB transmitters and transceivers as well.

As time went on and everything started becoming solid-state Astatic never bothered to change the amplifier board and it stayed the same until the day they finally stopped making the D104 and the stands all together. Many of the newer radios had even lower mic input impedances and today most are around 600-ohms. Even many of the solid-state CB’s made in the 1970’s and 1980’s were a bad impedance match for the 5K to 6K and were being severely overdriven by the amplifier. Those 2-transistor amplified boards became nothing more than great little distortion amplifiers, but Astatic never cared. It made CB’ers happy so why change it?

Somewhere down the line from the 1930’s until about the 1960's most of the D104 crystal elements themselves remained around 20Meg. I think it was sometime around the mid 1960’s Astatic did manage to reduce the impedance down to around 10Meg, but they never went down any lower than that. The last D104’s sold had 10M crystal elements that produce around a 4Vp-p max voltage swing. The ones with the amplifier boards are around 5K to 6K. The problem is when you try to connect one to a modern radio that has the typical impedance of only 600-ohms. Well, with a 10Meg crystal element and a 600-ohm load it’s not going to work very well. The stock amplifiers boards with the 5K to 6K output will work a little better, but it will still have insufficient low-end response and it will severely overdrive the input. Again, great little distortion amplifiers. The solution is to remove that stock 2-transistor amplifier in the base of the stand and replace it with the simple FET source follower buffer transistor circuit. FET transistors have high input impedances whereas BJT transistors have low input impedances so it must be an FET (JFET) transistor.

Anyway, that’s the correct story and information. You will find a lot of mis-information about it on the web..